A terminal in a wireless communication system (e.g., a cellular phone in a cellular system) is typically designed to operate at any given moment in one of several modes, such as active and idle modes. In the active mode, the terminal can actively exchange data with one or more base stations belonging to the system (e.g., for conducting a voice or data call). In the idle mode, which may also be referred to as a standby mode, the terminal typically monitors a channel (a paging channel) for messages alerting the terminal to the presence of incoming calls. The wireless mobile network typically requires the terminal to be in idle mode for relatively long periods in order to reduce the traffic load due to carrying out unessential processes in the network.
In more details, when determined that a current mode is not an active mode, individual terminals operating in such a conventional cellular network remain in an idle mode and are occasionally awaken from the idle mode to check reception of paging signals addressed to them. If the paging signal is transmitted to any one of the terminals, that terminal would change its own mode to an active mode. Otherwise, when no paging signal has been transmitted to the terminal, it would re-enter the idle mode.
Now, even though they may be in idle mode, mobile wireless terminals can move from one location to another. As a result, the location of a moving terminal may change while being in an idle mode, and when the terminal wakes up, it can no longer communicate with the base station it communicated before entering the idle mode, and will have to communicate through a different base station. Typically, when changing base stations, a wireless terminal is expected to conduct a “handoff” process whereby the new base station is contacted, and arrangements are made for this new base station to serve the wireless terminal. When a wireless terminal is in an active, such a procedure will be followed. But, when the wireless terminal is in an idle mode, this is typically not the case. Such handoffs are power consuming and make use of the system resources that could otherwise be used to carry data traffic. Furthermore, it could well be that a mobile terminal enters an area serviced by another, a second base station while being in a sleep mode, and will leave that area to an area serviced by a further, a third base station, before awakening. In such a case, all resources allocated to by the second base station to service the terminal are wasted for no good reason. To avoid these penalties, prior art systems have defined “paging areas” in which an idle wireless terminal need not conduct a handoff. Instead, all of the base stations located within the paging area will broadcast the paging messages addressed for the idle wireless terminal. The wireless terminal then needs only to tune its receiver to the base station from which the best signal is received and continue communicating through that base station. A central controller keeps track of which paging area each wireless terminal is in.
Several methods and solutions addressing certain aspects of this type of operation have been suggested in the art.
US 20050048982 discloses the use of a controller for wireless communication system, which receives sufficient system information to process paging channel for a base station, prior to the completion of cell reselection procedure.
EP 1124399 discloses a paging method for wireless terminals that involves assigning new paging agent to the wireless terminal. When the wireless terminal assigned with the paging agent moves outside the paging area, the wireless terminal is provided with the capability to define its own “personal” paging area using a list of all the base stations that it knows.
WO 0207459 discloses several techniques for a terminal to efficiently process paging channels in an asynchronous wireless communication system. If the base stations are not synchronized with each other and a remote terminal's designated paging time is different from one base station to another, the remote terminal can wake up based on the earliest base station paging time in a reacquisition search list that includes candidate base stations to which the remote terminal may be handed off. The criteria to select base stations for evaluation as reacquisition targets, may be based on the received power of the signals received from the various base stations as well as on their timing, where both of these parameters may be made relative to that of a preferred base station. Also, the remote terminal may wake up a number of times in a particular paging cycle if there are one or more candidates base station to which the remote terminal may be handed off.
WO 05022781 discloses an apparatus for controlling a sleep mode in a wireless access communication system which involves determining paging interval type of specific subscriber terminal, based on paging interval types and sleep request message received from specific terminal. The subscriber terminal is registered in one of the groups determined on the basis of the paging interval type of the subscriber terminal. Upon receipt of the group information, the apparatus controls a base station to pre-recognize a terminal woken up at a predetermined time from among a plurality of terminals entering the sleep mode, resulting in reduction of the number of unnecessary paging message transmissions and improved efficiency of the wireless access communication system.
Current mobile networks use a centralized entity for controlling paging operations to mobile terminal(s) being in idle mode. However, this solution is not an adequate solution to networks where the number of mobile terminals is rapidly growing as the time and resources required to support such a centralized entity to properly function increase dramatically.